The present invention relates to an automatic transmission employing a torque converter as a starting element, and more particularly to an automatic transmission which controls an engagement force of a clutch such as a forward clutch using an actuator for a lockup clutch hydraulic control.
Japanese Published Patent Application No. 7-269667 discloses an automatic transmission which employs a torque converter as a starting element. It is generally necessary to set an engagement capacity of a forward clutch at a value greater than a product of an engine torque and a stall torque ratio of a forward clutch. The forward clutch is designed so that a piston thereof has a large outer diameter to ensure a sufficient engagement capacity.